Manoeuvring mathematical model for "Ship Docking Module (SDM)"

During a real-time simulation study of escort manoeuvres of a “Ship Docking Module (SDM™)”, the manoeuvring characteristics of an escort tug were investigated. The tug is designed with two azimuthing thrusters that have an asymmetric lay-out on the hull. The operational mode of the tug requires sailing at very high drift angles. To simulate the manoeuvring characteristics of this type of operation, captive tests using a Planar Motion Mechanism (PMM) were performed to derive the manoeuvring mathematical model with interaction components between various components such as skegs and thrusters. To validate the derived mathematical model free-sailing manoeuvring tests were also performed. For the bare hull model, terms for very high drift angles were found and modeled as well as thruster-thruster interaction effects due to the axe-symmetric configuration which were found to be significant during the test series. The results of the free-sailing model tests were compared to the manoeuvring simulations carried out with the numerical model. These manoeuvring calculations were conducted using an adapted version of the latest release of the manoeuvring simulation program SURSIM. The comparison between measurements and simulations indicated that the yaw checking and initial turning characteristics as well as steady state turning characteristics are very well replicated by the numerical model. Additional spiral manoeuvres were conducted to obtain the full relationship between the helm angle and the motion response. A high directional stability was observed for the vessel. Further validation includes the rpm-speed curves of the ship for both longitudinal and transverse sailing conditions and the bollard pull against rpm plots to evaluate the initial response of the ship from an escorting point of view. The derived mathematical model will be used for full mission bridge simulations for crew training in the future.